1. Field of the Invention
The present invention relates to a pressure incubator, and more particularly to a pressure incubator used for incubating cells or aerobic microorganisms in vitro to a high density.
2. Description of the Prior Art
In order to incubate cells or aerobic microorganisms in vitro to a high density, it is necessary to supply a sufficient amount of oxygen to the medium in a culture vessel and to fully replace the medium in order to remove the waste matter produced in the medium and to replenish the medium with nutrients. To meet the first requirement, there is an apparatus known for incubating cells at atmospheric pressure in the presence of hemoglobin, fluorocarbon or the like and which is capable of dissolving oxygen in an amount 20 times the amount soluble in water as an O.sub.2 carrier (Yukio Sugino, "Cell Incubation Techniques," Kohdansha, 1985, p. 133). Also known is an apparatus which comprises a tube for introducing gaseous oxygen into the space above the culture medium or into the medium within a culture vessel to bring the gas into contact with the medium or bubble the gas through the medium at atmosphere pressure. To meet the second requirement, the cells must be separated from the culture by directly filtering the cell-containing or by using a cell sedimentation tube utilizing the fact that the cells have a greater specific gravity than the medium (the same publication as above, p. 148).
However, when an additional substance is incorporated into the medium, there arises a need to resort to a cumbersome procedure for collecting the product from the medium and isolating the product in a purified form, while the result achieved by the supply of oxygen gas into the space above the medium is dependent on the speed of agitation of the medium. The introduction of oxygen gas into the medium is efficient, but excess bubbles in the medium destroy the cells. Thus, the above apparatus or methods each have different problems associated with them.
On the other hand, direct filtration of the culture to separate the cells from the medium rapidly clogs the filter, which is therefore not usable for a prolonged period of time, while the cell sedimentation tube must be used at a uniform ambient temperature. Otherwise, convection will occur, making it impossible to separate the cells from the medium. Further because the quantity of medium that can be separated off is limited by the settling rate of cells, high-density incubation encounters the problem that the medium can not be changed as frequently as is desired.
One object of the present invention, which has been accomplished in view of the foregoing situation, is to provide a pressure incubator wherein oxygen gas can be supplied to the culture efficiently using no additive and without destroying the cells. Another object of the invention is to provide a pressure incubator which is so adapted that the medium in a culture vessel can be fully replaced.